I think the main difference is just that Path only lets you follow such a small number of people. Thus you are immediately saying these people are credible to you & whatever links they share are most likely worth looking into. Versus Foursquare where each link posted is just another drop in the hat for people how have hundreds or thousands of people they follow.
That IS a difference, but I don't follow anyone on Path (yet). The Path links I consume are via Twitter, as were the Foursquare ones, so arguably the credibility and selection bias are equalized.
Since the links I consume have been shared on Twitter (by people who don't follow me, and whom I don't follow) people are breaking out of the Path limitations by automatically, simultaneously publishing their updates to Twitter as they're being posted on Path. Effectively people have subverted the 'private' differentiation the Path offers in a lot of use cases from what I am seeing.
